A number of techniques have been developed to track the position of a mobile object (e.g., people, vehicles, pets) on the earth's surface at any given time. Perhaps the best known technique involves the global positioning system (“GPS”). GPS technology uses transmitters carried by orbiting satellites. A receiver mounted on the mobile object that is being tracked polls the signals transmitted by the satellite to calculate its distance from that satellite. The receiver applies triangulation by detecting signals from three or more GPS satellites to determine its own latitude and longitude on the earth's surface, or from four or more GPS satellites to determine its latitude and longitude, and also its altitude.
Such a position tracking device outputs a specific, precise latitude/longitude/altitude datapoint. For purposes of the discussion presented herein, it should be understood that the term “position” refers to the geographic counterpart of a particular datapoint.
Because every position tracking technology has some inherent inaccuracy, including GPS, the calculated position will often fluctuate around the object's true position. Furthermore, something having a meaningful geographic significance to a person (such as a street address) often does not have a sharply defined boundary. To remedy these problems, an appropriate technique is applied to group together nearby positions to be treated as a single geographic “location”. Thus, the term “location” as used herein refers to a single position or a plurality of nearby positions corresponding to each other in some way, and perhaps having some meaningful significance to a person. One technique for identifying positions that deserve to be grouped together is called clustering. More information on the significance of these terms (i.e. position, location, clustering) and how such information is useful for the present invention is set forth in co-pending, commonly-owned U.S. patent application Ser. No. 10/751,058 filed Dec. 31, 2003 and titled “TECHNIQUE FOR COLLECTING AND USING INFORMATION ABOUT THE GEOGRAPHIC POSITION OF A MOBILE OBJECT ON THE EARTH'S SURFACE”, the content of which is hereby incorporated by reference.
A person utilizing the present invention will not normally know a precise datapoint and will more likely use an address of some type which, as explained above, involves a cluster of positions referred to as a location. Therefore, the term “position” is used herein in connection with the precise data outputted by a tracking device while, in contrast, the term “location” is used herein (in addition to being the output of the cluster algorithm) as convenient shorthand (with its meaning being clear from the context) to refer to any position, location or region (this term is discussed below) specified by the sender for the purpose of automatic message delivery to a recipient.
Tracking an object has been used not only to know the object's current position at any given time but also for the purpose of conveying information. For example, U.S. Pat. No. 5,760,742 uses GPS technology to create and annotate GIS (Geographic Information Systems) databases. A vehicle carrying the apparatus can receive geographic information transmitted from a base station specific to a designated location, and the operator can also transmit to the base station geographic information concerning a certain location to update or enhance the previously available geographic information for that location. Also, the game of geocaching (information about it is available at www.geocaching.com) is based on placing caches at specified locations that contain prizes and/or information which can be obtained when (if) the cache is found. GPS units are used to play geocaching. However, none of the known location-based techniques serves to, in effect, enable a sender to leave a message for an intended recipient “floating in the air” at a particular location just waiting for the intended recipient to arrive, at which time the message becomes automatically “visible”.